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Amplifiers that run from an brad bord to a BS2 — Parallax Forums

Amplifiers that run from an brad bord to a BS2

Ferris_BueFerris_Bue Posts: 40
edited 2007-10-04 16:20 in Learn with BlocklyProp
Hey all,

I need some help. I'm needing to build a amp to make the sound lader or softer. I was also wording if a Class A or a Type A amp would work better for what I'm doing? I have some idea but not to sure. Need help on this.

Ferris!!!!

Comments

  • ZootZoot Posts: 2,227
    edited 2007-09-26 23:32
    The attached schematic lets you run an 8-ohm speaker at a pretty loud volume from a Stamp pin. It uses an LM386 -- a commonly available audio amp chip that you can get at Radio Shack for a few dollars.

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    When the going gets weird, the weird turn pro. -- HST
    ParallaxAudioAmpCircuit.jpg
    720 x 280 - 55K
  • Ferris_BueFerris_Bue Posts: 40
    edited 2007-09-27 15:19
    So your saying is that a Type A amp is better than a Class A amp there this. Do you have to run it at 5 vots and is there a way to cut out the ext speaker and the thing right below it? B/c I you can I would like to know about it.

    Ferris!!!

    Post Edited (Ferris_Bue) : 9/27/2007 4:27:02 PM GMT
  • Steph LindsaySteph Lindsay Posts: 767
    edited 2007-09-27 16:50
    Hey, are you trying to amplify a little piezospeaker like we include in the WAM kit, or a different kind?· Andy wrote a Stamps in Class·Mini-Project for amplifying the piezospeaker (see the blue sticky-thread at the top of the forum).· That app is posted here:

    http://forums.parallax.com/showthread.php?p=560570

    -Stephanie
  • Ferris_BueFerris_Bue Posts: 40
    edited 2007-09-27 20:08
    Ummmmm, no not the piezo. More along the lines of a small speaker but bigger then the piezo.


    Ferris!!!!
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2007-09-28 12:24
    http://www.radioshack.com/product/index.jsp?productId=2062620&cp
  • Mike GreenMike Green Posts: 23,101
    edited 2007-09-28 14:25
    The Class of an amplifier indicates how it reproduces the input signal and how efficient it is. Class A linearly amplifies the input signal and is the least efficient. Class B amplifies only the positive (or negative) halves of the waveforms and is more efficient. Class C amplifies only a portion of the signal and is the most efficient - it's usually used for RF where a tank (resonant) circuit will provide the rest of the waveform.

    I think the LM386 is Class AB. It doesn't work very well at 5V and really needs at least 6V.

    Class D is used to describe PWM based digital amplifiers.
  • Ferris_BueFerris_Bue Posts: 40
    edited 2007-09-28 15:07
    Well I went with a Type A amp. I have use the lm386 with 5 volts and to me it was a little soft. I did go with the pic at the top of this page.

    Ferris!!!!
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2007-09-28 15:38
    Add the "gain capacitor" (see attached drawing) between pin 1 and pin 8.
    more gain.JPG
    492 x 398 - 19K
  • Ferris_BueFerris_Bue Posts: 40
    edited 2007-09-28 16:12
    So with the pin out is there a differance bettwen haveing pin2 going to the pot and having pin3 to ground or haveing pin3 to the pot and haveing pin2 to ground? I havetryed it both ways and it makes no differance. Can you guys clare this up.

    Ferris!!!!
  • ZootZoot Posts: 2,227
    edited 2007-09-29 22:13
    Pin 2 of the LM386 is the - input, so since you are probably not providing a true differential input, you need to tie that pin to ground. Pin 3 is the + input -- essentially it receives the FREQOUT signal from your Stamp. The pot is your volume control. Very necessary.

    The gain cap PJ suggested will boost output further -- if you do this I would just make sure that a) you run the circuit from at least 6v (9v is better) and that you check your speaker to see what kind of a wattage it will handle. With the boost cap, don't use one of those cheapo 100mw 8ohm speakers from Radio Shack -- the distortion will be terrible and you may blow the speaker. If memory serves (I am in Jackson Hole right now and don't have the specs in front me), with the boost cap and 9v you will have an amp on the order of 800mw - 1000mw. Without the boost cap, I believe the amp is more on the order of 300-500mw.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    When the going gets weird, the weird turn pro. -- HST
  • Ferris_BueFerris_Bue Posts: 40
    edited 2007-10-01 15:32
    Thanks, for that. That cleard that up for me. But also why do I need a bigger cap when I have a gain of 200? Right now I have the 220 in and it works fine.

    Ferris!!!!

    Post Edited (Ferris_Bue) : 10/1/2007 4:20:13 PM GMT
  • ZootZoot Posts: 2,227
    edited 2007-10-01 21:14
    PJ was talking about about the cap between pins 1 and 8 of the LM386, not the 220 cap between the amp output and the speaker. The optional cap and/or resistor between pins 1 and 8 is the overall gain control. You may not need this. See the LM386 spec sheet (attached).

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    When the going gets weird, the weird turn pro. -- HST
    pdf
    pdf
    LM386.pdf
    298K
  • Ferris_BueFerris_Bue Posts: 40
    edited 2007-10-02 15:41
    Hey zoot,
    Can you replace the doc that you put up. Its not leting me see it.

    Ferris!!!!
  • ZootZoot Posts: 2,227
    edited 2007-10-02 21:26
    Hmm... I just downloaded it from the site and it worked fine when I opened it in Acrobat Reader (it's a PDF).

    Do you have Reader installed? Can you read PDFs? If not, visit www.adobe.com/products/acrobat/readstep2.html.

    Or do a search for LM386 at either Jameco.com or Digikey.com and you'll get links to their posted copies of the spec sheet.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    When the going gets weird, the weird turn pro. -- HST
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2007-10-03 10:11
    By the way, I think that Type A and Class A are the same kind of amplifier.

    Amplifiers are usually classified into A, B, and AB.

    Class or Type A usually consume more power inorder to produce a more precise signal.

    The LM386 has a document that explains it. Without a capacitor between PIN 1 and PIN 8, it will amplify at 20 times the original input. With a 10mf capacitor, it will go up to 200 times.
    If you don't need the extra amplification, just leave it out. If you want somewhere between 20 and 200 times, you have to add a resistor in line with the capacitor and an adjustibe resistor is more convienent.

    The amplifier will work at +5 volts just fine, but a higher voltage provides more power and possibly a cleaner sound.

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    "Everything in the world is purchased by labour; and our passions are the only causes of labor." -- David·Hume (1711-76)········
    ···················· Tropically,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan

    Post Edited (Kramer) : 10/4/2007 10:21:02 AM GMT
  • Ferris_BueFerris_Bue Posts: 40
    edited 2007-10-03 14:32
    Nice, thanks for that. Like I keep saying, if anyone can help I would like it.

    Ferris
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2007-10-04 10:31
    Ferris-Blue,
    Zoot provided a link to the LM386.PDF file. If you can read that, it will help a great deal. It is complete and necessary information.

    Regarding Class A, Class B, and Class AB amplifyers - Class A are the best at producing an exact copy of the orignal audio. Class B and Class AB save power by not producing as good a quality reproduction,·sometimes clipping the peaks of the signal.· There are Class C and Class D amplifiers too.

    The LM386 is the right chip for a 0.3 watt audio amp for 8 ohm speaker with a +5 to +12volt supply. And the schematic Zoot provided is the right design for a BasicStamp as it includes a low pass filter to make it sound better. You can use a 4 ohm or 16 ohm speaker without trouble.

    P.J. Allen copied an example from the LM386.PDF to show you where to put the 10uf capacitor to increase the gain. See the red arrow. I really don't think you need to have Gain = 200 from the BasicStamp. It may just·cause distortion and no real increase in volume. I am trying to build the Gain = 20 set up right now.

    If you don't understand basic amplifiers, try Wikipedia for 'amplifier' to get the basics. Or find a good introductory text for electronics.

    And I repeat -Type A and Class A are the same thing.

    You can do the same thing with a few transistors, but the LM386 makes it so easy.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    "Everything in the world is purchased by labour; and our passions are the only causes of labor." -- David·Hume (1711-76)········
    ···················· Tropically,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan

    Post Edited (Kramer) : 10/4/2007 10:40:56 AM GMT
  • Ferris_BueFerris_Bue Posts: 40
    edited 2007-10-04 14:35
    Like I keep saying any help is good.

    Ferris!!!!
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2007-10-04 16:20
    Ferris_Blue,
    I suggested Wikipedia for help with amplifiers, but this is much better.

    http://www.tscm.com/NEETS-v08-Amplifiers.pdf

    This is what the U.S. Navy uses to train sailor electronic technicians. Fortunately, all the NEETS training manuals are free to the public because there is no copyright protection for U.S. Goverment publications.

    If you want all the different topics, go to
    http://www.zianet.com/NMAMARS/downloads/neets.htm

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    "Everything in the world is purchased by labour; and our passions are the only causes of labor." -- David·Hume (1711-76)········
    ···················· Tropically,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan
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